arXiv subjects

Anamul Md. Hoque

Publications and source records attributed to Anamul Md. Hoque.

12 recordsLinked to original sources

arXiv2024

Room temperature nonlocal detection of charge-spin interconversion in a topological insulator

Topological insulators (TIs) are emerging materials for next-generation low-power nanoelectronic and spintronic device applications. TIs possess non-trivial spin-momentum locking features in the topological surface states in addition to the spin-Hall effect (SHE), and Rashba states due to high spin-orbit coupling (SOC) properties. These phenomena are vital for observing the charge-spin conversion (CSC) processes for spin-based memory, logic and quantum technologies. Although CSC has been observed in TIs by potentiometric measurements, reliable nonlocal detection has so far been limited to cryogenic temperatures up to T = 15 K. Here, we report nonlocal detection of CSC and its inverse effect in the TI compound Bi1.5Sb0.5Te1.7Se1.3 at room temperature using a van der Waals heterostructure with a graphene spin-valve device. The lateral nonlocal device design with graphene allows observation of both spin-switch and Hanle spin precession signals for generation, injection and detection of spin currents by the TI. Detailed bias- and gate-dependent measurements in different geometries prove the robustness of the CSC effects in the TI. These findings demonstrate the possibility of using topological materials to make all-electrical room-temperature spintronic devices.

cond-mat.mes-hall↗

arXiv2023

Large out-of-plane spin-orbit torque in topological Weyl semimetal candidate TaIrTe4

Topological quantum materials, with novel spin textures and broken crystal symmetries are suitable candidates for spintronic memory technologies. Their unique electronic properties, such as protected surface states and exotic quasiparticles, can provide an out-of-plane spin polarized current needed for external field free magnetization switching of magnets with perpendicular magnetic anisotropy. Conventional spin-orbit torque materials, such as heavy metals and topological insulators, provide only an in-plane spin polarized current, and recently explored materials with lower crystal symmetries provide very low out-of-plane spin polarized current components, which is not suitable for energy-efficient spin-orbit torque (SOT) applications. Here, we demonstrate a large out-of-plane damping-like SOT at room temperature using a topological Weyl semimetal candidate TaIrTe4 with a lower crystal symmetry. We performed spin-orbit torque ferromagnetic resonance (STFMR) experiments in a TaIrTe4/Ni80Fe20 heterostructure and observed a large out-of-plane damping-like SOT efficiency. The out-of-plane spin Hall conductivity is estimated to be an order of magnitude higher than the reported values in other materials. These findings of high spin Hall conductivity and large out-of-plane SOT efficiency are suitable for the development of energy efficient and external field-free spintronic devices.

cond-mat.mes-hall↗

arXiv2022

Charge to Spin Conversion in van der Waals Metal NbSe2

Quantum materials with a large charge current-induced spin polarization are promising for next-generation all-electrical spintronic science and technology. Van der Waals metals with high spin-orbit coupling and novel spin textures have attracted significant attention for an efficient charge to spin conversion process. Here, we demonstrate the electrical generation of spin polarization in NbSe2 up to room temperature. To probe the current-induced spin polarization in NbSe2, we used a graphene-based non-local spin-valve device, where the spin-polarization in NbSe2 is efficiently injected and detected using non-local spin-switch and Hanle spin precession measurements. A significantly higher charge-spin conversion in NbSe2 is observed at a lower temperature, below the superconducting transition temperature Tc ~ 7 K of NbSe2. However, the charge-spin conversion signal could only be observed with a higher bias current above the superconducting critical current, limiting the observation of the signal only to the non-superconducting state of NbSe2. Systematic measurements provide the possible origins of the spin polarization to be predominantly due to the spin Hall effect or Rashba-Edelstein effect in NbSe2, considering different symmetry allowed charge-spin conversion processes.

cond-mat.mes-hall↗

arXiv2021

Multifunctional Spin Logic Gates In Graphene Spin Circuits

All-spin-based computing combining logic and nonvolatile magnetic memory is promising for emerging information technologies. However, the realization of a universal spin logic operation representing a reconfigurable building block with all-electrical spin current communication has so far remained challenging. Here, we experimentally demonstrate a reprogrammable all-electrical multifunctional spin logic gate in a nanoelectronic device architecture utilizing graphene buses for spin communication and multiplexing and nanomagnets for writing and reading information at room temperature. This gate realizes a multistate majority spin logic operation (sMAJ), which is reconfigured to achieve XNOR, (N)AND, and (N)OR Boolean operations depending on the magnetization of inputs. Physics-based spin circuit model is developed to understand the underlying mechanisms of the multifunctional spin logic gate and its operations. These demonstrations provide a platform for scalable all-electric spin logic and neuromorphic computing in the all-spin domain logic-in-memory architecture.

cond-mat.mes-hall↗

arXiv2021

Van der Waals Magnet based Spin-Valve Devices at Room Temperature

The discovery of van der Waals (vdW) magnets opened up a new paradigm for condensed matter physics and spintronic technologies. However, the operations of active spintronic devices with vdW magnets are so far limited to cryogenic temperatures, inhibiting its broader practical applications. Here, for the first time, we demonstrate room temperature spin-valve devices using vdW itinerant ferromagnet Fe5GeTe2 in heterostructures with graphene. The tunnel spin polarization of the Fe5GeTe2/graphene vdW interface is detected to be significantly large ~ 45 % and negative at room temperature. Lateral spin-valve device design enables electrical control of spin signal and realization of basic building blocks for device application such as efficient spin injection, transport, precession, and detection functionalities. Furthermore, measurements with different magnetic orientations provide unique insights into the magnetic anisotropy of Fe5GeTe2 and its relation with spin polarization and dynamics in the heterostructure. These findings open opportunities for the applications of vdW magnet-based all-2D spintronic devices and integrated spin circuits at ambient temperatures.

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arXiv2020

Robust Spin Interconnect with Isotropic Spin Dynamics in Chemical Vapour Deposited Graphene Layers and Boundaries

The utilization of large-area graphene grown by chemical vapour deposition (CVD) is crucial for the development of scalable spin interconnects in all-spin-based memory and logic circuits. However, the fundamental influence of the presence of multilayer graphene patches and their boundaries on spin dynamics has not been addressed yet, which is necessary for basic understanding and application of robust spin interconnects. Here, we report universal spin transport and dynamic properties in specially devised single layer, bi-layer, and tri-layer graphene channels and their layer boundaries and folds that are usually present in CVD graphene samples. We observe uniform spin lifetime with isotropic spin relaxation for spins with different orientations in graphene layers and their boundaries at room temperature. In all the inhomogeneous graphene channels, the spin lifetime anisotropy ratios for spins polarized out-of-plane and in-plane are measured to be close to unity. Our analysis shows the importance of both Elliott-Yafet and Dyakonov-Perel mechanisms, with an increasing role of the latter mechanism in multilayer channels. These results of universal and isotropic spin transport on large-area inhomogeneous CVD graphene with multilayer patches and their boundaries and folds at room temperature prove its outstanding spin interconnect functionality, beneficial for the development of scalable spintronic circuits.

cond-mat.mes-hall↗

arXiv2020

Charge-spin conversion signal in WTe2 van der Waals hybrid devices with a geometrical design

The efficient generation and control of spin polarization via charge-spin conversion in topological semimetals are desirable for future spintronic and quantum technologies. Here, we report the charge-spin conversion (CSC) signals measured in a Weyl semimetal candidate WTe2 based hybrid graphene device with a geometrical design. Notably, the geometrical angle of WTe2 on the graphene spin-valve channel yields contributions to symmetric and anti-symmetric CSC signal components. The spin precession measurements of CSC signal at different gate voltages and ferromagnet magnetization shows the robustness of the CSC in WTe2 at room temperature. These results can be useful for the design of heterostructure devices and in the architectures of two-dimensional spintronic circuits.

cond-mat.mes-hall↗

arXiv2020

Unconventional charge-spin conversion in Weyl-semimetal WTe2

An outstanding feature of topological quantum materials is their novel spin topology in the electronic band structures with an expected large charge-to-spin conversion efficiency. Here, we report a charge current-induced spin polarization in the type-II Weyl semimetal candidate WTe2 and efficient spin injection and detection in a graphene channel up to room temperature. Contrary to the conventional spin Hall and Rashba-Edelstein effects, our measurements indicate an unconventional charge-to-spin conversion in WTe2, which is primarily forbidden by the crystal symmetry of the system. Such a large spin polarization can be possible in WTe2 due to a reduced crystal symmetry combined with its large spin Berry curvature, spin-orbit interaction with a novel spin-texture of the Fermi states. We demonstrate a robust and practical method for electrical creation and detection of such a spin polarization using both charge-to-spin conversion and its inverse phenomenon and utilized it for efficient spin injection and detection in a graphene channel up to room temperature. These findings open opportunities for utilizing topological Weyl materials as non-magnetic spin sources in allelectrical van der Waals spintronic circuits and for low-power and high-performance non-volatile spintronic technologies.

cond-mat.mes-hall↗

arXiv2020

Gate-tunable Spin-Galvanic Effect in Graphene Topological insulator van der Waals Heterostructures at Room Temperature

Unique electronic spin textures in topological states of matter are promising for emerging spin-orbit driven memory and logic technologies. However, there are several challenges related to the enhancement of their performance, electrical gate-tunability, interference from trivial bulk states, and heterostructure interfaces. We address these challenges by integrating two-dimensional graphene with a three-dimensional topological insulator (TI) in van der Waals heterostructures to take advantage of their remarkable spintronic properties and engineer proximity-induced spin-charge conversion phenomena. In these heterostructures, we experimentally demonstrate a gate tunable spin-galvanic effect (SGE) at room temperature, allowing for efficient conversion of a nonequilibrium spin polarization into a transverse charge current. Systematic measurements of SGE in various device geometries via a spin switch, spin precession, and magnetization rotation experiments establish the robustness of spin-charge conversion in the Gr-TI heterostructures. Importantly, using a gate voltage, we reveal a strong electric field tunability of both amplitude and sign of the spin-galvanic signal. These findings provide an efficient route for realizing all-electrical and gate-tunable spin-orbit technology using TIs and graphene in heterostructures, which can enhance the performance and reduce power dissipation in spintronic circuits.

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arXiv2020

Two-Dimensional Spintronic Circuit Architectures on Large Scale Graphene

Solid-state electronics based on utilizing the electron spin degree of freedom for storing and processing information can pave the way for next-generation spin-based computing. However, the realization of spin communication between multiple devices in complex spin circuit geometries, essential for practical applications, is still lacking. Here, we demonstrate the spin current propagation in two-dimensional (2D) circuit architectures consisting of multiple devices and configurations using a large area CVD graphene on SiO2/Si substrate at room temperature. Taking advantage of the significant spin transport distance reaching 34 μm in commercially available wafer-scale graphene grown on Cu foil, we demonstrate that the spin current can be effectively communicated between the magnetic memory elements in graphene channels within 2D circuits of Y-junction and Hexa-arm architectures. We further show that by designing graphene channels and ferromagnetic elements at different geometrical angles, the symmetric and antisymmetric components of the Hanle spin precession signal can be remarkably controlled. These findings lay the foundation for the design of complex 2D spintronic circuits, which can be integrated into efficient electronics based on the transport of pure spin currents.

cond-mat.mes-hall↗

arXiv2019

All-electrical creation and control of giant spin-galvanic effect in 1T-MoTe2/graphene heterostructures at room temperature

The ability to engineer new states of matter and to control their electronic and spintronic properties by electric fields is at the heart of the modern information technology and driving force behind recent advances in van der Waals (vdW) heterostructures of two-dimensional materials. Here, we exploit a proximity-induced Rashba-Edelstein (REE) effect in vdW heterostructures of Weyl semimetal candidate MoTe2 and CVD graphene, where an unprecedented gate-controlled switching of spin-galvanic effect emerges due to an efficient spin-to-charge conversion at room temperature. The magnitude of the measured spin-galvanic signal is found to be an order of magnitude larger than the other systems, giving rise to a giant REE. The magnitude and the sign of the spin-galvanic signal are shown to be strongly modulated by gate electric field near the charge neutrality point, which can be understood considering the spin textures of the Rashba spin-orbit coupling-induced spin-splitting in conduction and valence bands of the heterostructure. These findings open opportunities for utilization of gate-controlled switching of spin-galvanic effects in spintronic memory and logic technologies and possibilities for realization of new states of matter with novel spin textures in vdW heterostructures with gate-tunable functionalities.

cond-mat.mes-hall↗

arXiv2019

Observation of Spin Hall Effect in Weyl Semimetal WTe2 at Room Temperature

Discovery of topological Weyl semimetals has revealed the opportunities to realize several extraordinary physical phenomena in condensed matter physics. Specifically, these semimetals with strong spin-orbit coupling, broken inversion symmetry and novel spin texture are predicted to exhibit a large spin Hall effect that can efficiently convert the charge current to a spin current. Here we report the direct experimental observation of a large spin Hall and inverse spin Hall effects in Weyl semimetal WTe2 at room temperature obeying Onsager reciprocity relation. We demonstrate the detection of the pure spin current generated by spin Hall phenomenon in WTe2 by making van der Waals heterostructures with graphene, taking advantage of its long spin coherence length and spin transmission at the heterostructure interface. These experimental findings well supported by ab initio calculations show a large charge-spin conversion efficiency in WTe2; which can pave the way for utilization of spin-orbit induced phenomena in spintronic memory and logic circuit architectures.

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